If they upgraded to Windows 10, chances are the license is "gone" (as it should be).
If he calls the 1-800 number it's automated. It asks you to put in some numbers that appear on the screen, and spits out some numbers you enter back in the corresponding fields.
It's worth a try. Best case = W7 back (if that's what they want, for whatever reason), worst case = no further forward/behind and they need to reinstlal Windows 10, or buy a W7 license.